1. Field of the Invention
The present invention relates to a slide type continuous variable valve lift device.
2. Description of Related Art
As for an engine, a camshaft is rotated by a rotating force transmitted from a crank shaft, and an intake valve and an exhaust valve are reciprocated up and down with regular timing by cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power.
At this time, a device that can continuously vary the lift distance of a valve according to an operating speed of the engine is called a continuous variable valve lift (CVVL) device.
Hereinafter, a conventional CVVL device will be described in detail with reference to the attached drawings.
FIG. 1 is a schematic view illustrating the configuration of a conventional CVVL device.
The conventional CVVL device illustrated in FIG. 1 includes a swing arm 30, a cam lobe 40, a frame 50, a rocker arm 60 and a shaft coupler 70. The swing arm 30 is connected to a suction valve 10 and a hydraulic tappet 20 at respective opposite ends thereof, and has a swing arm roller 32 in the middle portion thereof. The cam lobe 40 is provided above the swing arm 30, and the frame 50 is provided to rotate coaxially with the cam lobe 40. The frame 50 has a cam follower 52 protruding out from one portion thereof, wherein a rounded surface 54 is formed in the inner surface of the cam follower 52. The rocker arm 60 is hinged to one portion of the swing arm 30 by a coupler 62, and is provided with a sliding block 66 on the upper end thereof which slides along the rounded surface 54 of the frame 50. The shaft coupler 70 is configured to rotate the frame 50.
A rocker roller 64 is provided on the upper portion of the rocker arm 60, in contact with the outer circumference of the cam lobe 40, and the rocker arm 60 is configured to rotate around the coupler 62 in response to the rotation of the cam lobe 40.
With the above-described configuration, when the cam lobe 40 rotates counterclockwise at the position shown in FIG. 1 so that the tip of the protrusion of the cam lobe 40 comes into contact with the rocker roller 64, the rocker arm 60 rotates clockwise around the coupler 62.
In this case, the center of curvature of the rounded surface 54 is located above the center of rotation of the frame 50. Thus, when the sliding block 66 provided in the upper end of the rocker arm 60 is pulled to the right, the frame 50 rotates in a clockwise direction. As a result, the sliding block 66 comes into contact with the upper portion of the rounded surface 54.
A drive cam 56 is formed in a portion of the frame 50, which comes into contact with the swing arm roller 32. When the frame 50 rotates clockwise at the position shown in FIG. 1, the swing arm 30 is pressed downwards by the drive cam 56 so as to rotate counterclockwise around the end portion connected to the hydraulic tappet 20. Then, the suction valve 10 is moved downwards thereby opening a channel to feed fuel into a cylinder.
Further, when the shaft coupler 70 rotates counterclockwise from the position shown in FIG. 1 thereby causing the frame 50 to rotate clockwise. The sliding block 66 also comes into contact with an upper portion of the rounded surface 54, which is higher than the position shown in FIG. 1. Further, the drive cam 56 is closer to the swing arm 32 than in the position shown in FIG. 1. When the cam lobe 40 rotates from this position to further rotate the frame 50 in a clockwise direction, the drive cam 56 further rotates the swing arm 30 to further increase the lift distance of the suction valve 10.
In other words, the conventional CVVL device shown in FIG. 1 can adjust the lift distance of the suction valve 10 by changing the angle of rotation of the frame 50 before the rocker arm 60 is rotated by the rotation of the cam lobe 40.
However, in the conventional CVVL device described as above, when the swing arm rotates following the rotation of the cam lobe, sliding friction may occurs in at least five places including the contacts between the cam lobe and the frame, between the cam lobe and the rocker roller, between the sliding block and the rounded surface, between the drive cam and the swing arm roller and between the swing arm roller and the swing arm. A large amount of power is lost by friction, and thus precise operation control becomes difficult.
Other problems include increasing the number of springs, which apply an elastic force to respective parts in order to constantly maintain the coupling positions of the respective parts, and increasing loss of friction of the respective parts
Furthermore, the friction loss of the respective parts is increased greatly due to the increased number of springs, which apply an elastic force to respective parts to constantly maintain the coupling positions of the respective parts.
Moreover, since the conventional CVVL device is made up of a large number of parts, it is difficult to fabricate the device, manufacturing costs are increased, and the overall robustness of the device becomes lower.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.